|Publication number||US7957931 B2|
|Application number||US 12/158,748|
|Publication date||Jun 7, 2011|
|Filing date||Oct 6, 2006|
|Priority date||Dec 23, 2005|
|Also published as||CA2634908A1, CA2634908C, CN101331384A, CN101331384B, EP1963786A1, EP1963786A4, EP1963786B1, US20090177416, WO2007073272A1|
|Publication number||12158748, 158748, PCT/2006/1136, PCT/SE/2006/001136, PCT/SE/2006/01136, PCT/SE/6/001136, PCT/SE/6/01136, PCT/SE2006/001136, PCT/SE2006/01136, PCT/SE2006001136, PCT/SE200601136, PCT/SE6/001136, PCT/SE6/01136, PCT/SE6001136, PCT/SE601136, US 7957931 B2, US 7957931B2, US-B2-7957931, US7957931 B2, US7957931B2|
|Inventors||Jonas Nilsagard, Olle Takman, Manne Stenberg|
|Original Assignee||Gcoder Systems Ab|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (9), Non-Patent Citations (1), Referenced by (2), Classifications (8), Legal Events (2)|
|External Links: USPTO, USPTO Assignment, Espacenet|
The present invention relates to a device, method and system for determining a position of an object and in particular to a vision based solution using a pattern comprising absolute position data.
Many different types of control devices have been constructed for various purposes. The most common control device is the so called mouse giving positioning variables in two dimensions for use in controlling operation of applications on a computer. Other interface control devices include the so called joystick which gives positioning variables also in two dimensions from the stick; however, by using extra buttons in conjunction with the stick it is possible to enhance the number of “positioning variables”, but it should be understood that this device physically only measures positioning variables in two dimensions. A trackball also delivers data for two dimensions; a game pad often uses a small joystick like handle for measuring positioning variables and may extend the range of the functionality of the controller to more control data by utilizing extra buttons; a steering wheel (for computer gaming) delivers data in one dimension.
In many solutions found, the control device only gives reference measurements and not absolute measurements, meaning that for an application relying on absolute coordinates of the control device to function properly complex computing is needed to continuously keep track of the location of the control device. Still such devices either need to be calibrated regularly or they will continuously build up an error that quickly may become critical depending on application.
Also in other technical areas apart from above mentioned control devices, positioning data is used for determining the position of an object, and in many cases absolute measuring solutions are used, however, they are often quite complex and not cost effective to be used in low cost applications. Vision based systems have been utilized previously and often used in conjunction with reference points, for instance in vision based positioning systems for determining the position of vehicles or objects in movement. These systems may be mounted on the vehicle or object determining the position using reference points in the surrounding area or on an external position determining the position using reference points on the vehicle or object. These systems generally are quite complex and demand high quality vision systems and high computational powers. Such a system is presented in U.S. Pat. No. 5,965,879 wherein an one-dimensional absolute optical linear or rotary encoder is shown. This solution uses identical fiducial markers for finding a position of an object. The fiducial position is calculated in one direction namely the direction of travel. Another such system is presented in U.S. Pat. No. 6,765,195 wherein a two dimensional absolute optical encoder is shown. This solution uses two different fiducial markers for determining the position of an object. The fiducials are identical across all encoded positions and arranged in a manner which is strictly periodic in each direction of travel. Both of these systems illustrate systems which need complex optical solutions and where size of patterns is of the order a few micrometers of dimension. They do not provide bending or rotational information either.
It is therefore an object of the present invention to provide an accurate and low cost device which provides absolute position data with relatively cost effective and non-complex technology and that can also provide even three or four dimensional position information (x, y, z, and rotation).
This is achieved in a number of aspects of the present invention wherein:
A first aspect, a position detecting system is provided, comprising:
The object may be a three dimensional object, wherein the pattern group is provided on a curved surface of the object.
Two pattern group lines may be located essentially parallel to each other at a distance (d) away from each other in a longitudinal direction of a shaft. Two cameras may be provided, each reading one of the two pattern group lines.
The position detecting system may further comprise at least one illumination device. The output strength of illumination from the illumination device may be controlled by the computational device.
The node parts and information parts may comprise at least one of a filled circle, a ring, or a ring with a center marking and/or the parts may be color coded.
The pattern group and camera may be located in an enclosure providing protection from environmental parameters.
The computational device may further be arranged to determine symmetrical center positions of node points using a vision based algorithm using gradient analysis. The symmetrical centre is determined for both node and information parts of the pattern.
The node parts may comprise a plurality of different types, for instance filled point, unfilled point, or unfilled point with a centre dot. The point may have a shape chosen from one of: circular, rectangular, quadratic, or triangular.
The information parts may comprise a plurality of different types, for instance filled point, unfilled point, or unfilled point with a centre dot.
The computational device may be arranged to determine a distance between the object and the image acquisition device by measuring at least one of the size of a node part, the size of an information part, the distance between two node parts, the distance between two information parts, and the distance between a node and an information part.
A second aspect of the present invention, a torque sensor, for measuring a torque in an object, the sensor comprising:
Yet another aspect of the present invention, a method for determining a position of an object is provided, comprising the steps of:
Still another aspect of the present invention, a computer program stored in a computer readable medium is provided for determining a position of an object by analyzing data indicative of a pattern group located on the object, wherein the data is received from a camera, characterized in that the computer program is arranged to determine geometrical center positions in at least two directions of node points in the pattern group for determining a position of the object relative the camera and further arranged to determine type and relative position of information points in the pattern group for determining location of the node points relative the object.
The symmetrical center positions of node points may be determined using a vision based algorithm using gradient analysis.
Yet another aspect is provided, an angular detector for determining an angular position of an object, comprising:
In the following the invention will be described in a non-limiting way and in more detail with reference to exemplary embodiments illustrated in the enclosed drawings, in which:
Signals from the image acquiring device 3 are transferred to a processing device 200, illustrated in
The processing device 200 may conveniently be situated within the measuring device it self or provided as an external stand alone device depending on application.
In the embodiment illustrated in
Non-contacting sensor means may advantageously be utilized since part of the object 2 is encapsulated within the casing 8 of the measuring device 1; however, these types of sensors may be used even if there is no encapsulation. Therefore, there is a small amount of disturbances that can influence the reading, such as dirt, light, or stray magnetic fields. In one embodiment the casing 8 is made of an electrically conducting material with magnetic shielding properties in order to reduce the risk of influencing a magnetic sensor measuring the position of the object 2. The pattern 4 and camera 3 may be provided in an enclosure for reducing the risk of contamination from the external environment, for instance dirt or light.
However, the invention is not limited to non-contacting measurements of the object's 2 position, contacting sensors can also be used, including, but not limited to, slip rings, impedance measurements, voltage dividers, digital encoders, and capacitive measurements.
Turning now to
Node points 301 to 304 may be as a ring 301, 302 or a ring with a dot 303, 304 inside (they may also be a filled circle). Node points 301 to 304 are used for determining the position in the camera window and type of point for a certain application and the determination is made in two steps: a first step for detecting the node points and a second for determining the node points' position with higher accuracy. The reason for doing the analysis in two steps is to reduce the computational power needed at each certain time unit. The more accurate determining may be made using a symmetry analysis, a centre of gravity analysis or similar method to determine the center of the point, a so called centroid calculation. This centroid calculation, using for instance gradient analysis, is done in at least two directions in order to acquire information about position in at least two directions (and possibly also rotational dimensionality of the object). The node points need to be large enough to provide a suitable number of pixels to do analysis on. In order to increase the accuracy of the determination the node points are advantageously not filled but rings with or without a dot in the center. This provides the analysis method chosen with a gradient feature both on the outside and the inside of the node point which enhances the accuracy of the center of the node analysis. The dot in the center of the ring may be used for providing a directional feature of the pattern, i.e. it will be easier for the analysis system since it will acquire reference points (or lines) on regular basis. These types of dot provided rings may be used every fifth degree around the object or so. For instance one may use undotted rings on an “equatorial” line of pattern groups and on each “southern” and “northern” 5 degrees from the “equatorial” line of pattern groups node points are used with dotted rings. Other shapes of the points may be used, for instance rectangularly or elliptically shaped points (these may be used for providing another way of obtaining directional and rotational information; i.e. the ellipse has a built in directional behavior from the shape). Other shapes may include quadratic, triangularly or irregularly shaped forms.
Information points 305 to 311 groups are centered around one node point, between two node points or between four node points. The information points are used for determining the absolute position of the pattern group. The information points have advantageously a different size than the node points in order to distinguish them from the node points. They are often smaller since they are not used for determining the position of the pattern with respect to the camera window but are used for determining the absolute coordinate of the identified group with respect to the object containing the pattern. Also these smaller information points may be of different character: filled circles, rings, and non existent (the non-existence of a point also provides information, if the system knows that a certain geometrical area may comprise points). The analysis system determines the pattern group of the information points and determines the relative position to each other and type of point character. Since the system knows the number of information points used in the information pattern groups, the system may determine which type of points is present at each location and from this analysis determine the absolute position of that information pattern group. Using seven information points as in
The pattern may be applied with any suitable application technique depending on type of surface and object, e.g. laser markings, engraving, etching, hobbing, knurling, scribing, dying, ink jet techniques, applied directly on the object or on a film or any other suitable material in turn fixed to the object, and so on as understood by the person skilled in the art. For instance an injection-molded sleeve may be provided with pattern groups already at the production of the sleeve and the sleeve may in turn be applied to an object of interest.
Points in the pattern group may have different depths and depth profiles in the material onto which the points are applied. This may be convenient for providing different contrast configurations. For instance a point with a conical narrowing depth wise will be seen by a camera as being darker than a point with a flat bottom surface. Also, the pattern may stand out from the object, for instance as cones sticking out from the material; this may be useful for instance for determining distance between the sensing device and the object.
The pattern may advantageously be arranged depending on type of surface, for instance to be suited for either essentially flat surfaces or curved surfaces. The present invention is particularly suited for use on curved surfaces.
The pattern may provide information about x and y position of the object as well as rotation or bending of the object in relation to the sensing device. By measuring the distance between two information or node points (or even between a node and information part) or the size of a code or node point it is also possible to determine the distance between the object and sensing device, i.e. the z position.
In case of an image acquisition device as sensing device an algorithm is used to determine the type of pattern and the relative positions and filling grade of each point. Since each pattern group is unique, it is possible to determine the absolute position of the pattern (and thus the object onto which the pattern is fixed). An analysis based on symmetry has benefits in being quick and not so computational intense and therefore possible to use in low cost solutions. The pixel values obtained from the camera comprise for instance grey scale data (or they may be color coded if the actual node and/or information points comprise color data), e.g. values in a range between 0 and 255. The analysis comprise setting a threshold value for where the system determines that a pixel comprise a marking or not. This threshold is settable (software or hardware vise) and may be controlled according to ambient light or dirt on the object upon where the markings are set. If a pixel completely is filled by a marked point, it may be read for example as 40 and a pixel completely without a marking may be read for example as 180, a pixel only partly filled by a marking may for example read as 90, which would be below a threshold of 100 and therefore determined as comprising a marking. It is possible to use these partly filled pixels in the analysis to enhance the accuracy of the position determination. The analysis scans over all pixels received in a frame and determines any node and information points in the frame. It may be arranged to filter out points below or over a certain number of pixels since the node and information points have a known size in pixels; e.g. points below 5 or larger than 15 may be filtered out for an application where node points have a size in the camera frame of ca 10 pixels and information points a size of ca 6 pixels. The present invention is not limited to the above exemplified values of grey scales and sizes of camera readings. This is very dependent on application and sought after accuracy of the system and may be varied in a wide range. For instance, in grey scale solutions, completely black may be represented by a 0 or a figure 255 and completely white with 255 or 0 accordingly. The pixel sizes of node and information points may be chosen to any other suitable value as understood by the person skilled in the art depending for instance on camera setting, application, and distance between the camera and the pattern.
The calibration method may comprise the following steps:
Adjustment of thresholds and lighting conditions may be utilized by reading background areas (i.e. areas without any pixels in) for obtaining a current light condition. It is then possible to set a new threshold value between marked or unmarked pixels and also it is possible to adjust the intensity from the illumination devices 320, 330, 340, 350 by controlling the light output from these illumination devices. One method of determining the background lighting conditions may be as follows: The camera frame window may be divided into 16 sectors and with the pattern exemplified earlier one may find four sectors where no points are present (or at least only partly present), one may find these four sectors by finding four virtual points 312-315 located between each node point on a line between node points (a line not comprising information points). The sectors where in these four virtual points are located may be used as background sectors for determining the background lighting conditions. A number of such readings may be used in a cumulative and averaging algorithm to enhance the accuracy of this background lighting determination. The number of sectors and background sectors are not limited to the above mentioned but different number of such sectors may be used.
Turning now to
In another variation of above described torque measuring device 710, the two cameras are reduced to one camera measuring on both patterns at the same time by relaying images to the camera from the two locations. This can be done by relaying the images using optical fibers, using mirrors, or a prism.
The camera may be an infrared sensitive camera detecting different temperatures in the object and the pattern on the object may be arranged with different temperature characteristics. Illumination in the infrared range may be provided in this type of solution in order to provide adequate illumination contrast and other parameters.
The present invention of determining absolute positions on objects may be utilized in a number of applications since the camera and computational systems may comprise low cost devices. Applications range from such as for instance a torque meter measuring torque in a non contact manner, for use in vehicles measuring torque in a shaft in the to drive line (for optimizing combustion processes or output power to each wheel) or in the steering wheel shaft (for use in power steering), in a bicycle (e.g. a spinning cycle used for exercise purposes), on any type of shaft where toque is of interest to measure. The invention may also be used for measuring other parameter related to a position of the object of interest, such parameters include, but are not limited to, force, rotational speed, position, and bending. The present invention may be used for instance also as a sensor for ABS (Automatic Break Systems) application, for anti spin sensors, or in CNC (computerized numerical control) machines in manufacturing for positioning the tool used in the CNC machine.
A one camera solution measuring pattern groups on an object with only rotational translation will provide an accurate and low cost solution for determining the angular position of the object, for instance as an angular encoder but with a large increase in resolution. For instance where the object is a wheel like object, e.g. a disc with a thickness sufficient enough to provide space for the pattern, the pattern may be provided on the wheel outer circumference or on a side of the wheel.
The present invention may be utilized in an articulating arm (for determining and digitizing the geometrical proportions of an object) by combining a number of different embodiments of the present invention. An articulating arm often comprises a number of joints, each with a position sensor for determining the position of each part comprising the arm. With a number of such angular joints the articulating arm can be used for determining the geometrical dimensions of the object and providing these to a computer aided design system (CAD) for obtaining the geometrical dimensions into a computational system. An articulating arm according to the present invention may comprise joints with a combination of 3D and 1D sensing devices, for instance a first 1D sensor located at the base of the arm, a second 1D sensor in each 1D joint between each arm section, and a 3D sensing device holding a probe used for determining the position of an test object under scrutiny of the articulating arm. The number and type of sensing devices forming part of the articulating arm may be varied in our configurations accomplishing the same functionality. The first 1D sensing device keeps track of the overall rotational position of the arm with respect to the surface where upon the articulating arm arrangement stands on, the second and subsequent 1D sensing devices in each joint between each arm section each keep track of a rotation position, and the 3D sensing device keeps track of the probe position relative the arm. Taking measurements from each sensing device into consideration the position of the probe relative the test object may be determined and the geometrical configuration of the test object digitized.
The present invention may also be used in a theodolite which is an instrument for measuring both horizontal and vertical angles, for instance for use in triangulation applications. The theodolite comprises a telescope mounted in such a manner as to be movably within two perpendicular axes: a horizontal axis and a vertical axis. The theodolite is often mounted on a tripod placed precisely and vertically over the point to be measured and its vertical axis aligned with local gravity. The present invention may be used for acquiring absolute positioning data for the theodolite with respect to the environment, for instance the ground position where upon the theodolite is centered above. The sensing system may be arranged as an intermediate joint between a base plate of the tripod and the telescope. However, it should be understood by the person skilled in the art that other parts and enclosures may be provided in order to build up such a device, for instance mechanical adjustment knobs for mechanically calibrate the device to a suitable position with respect to gravity and/or planar to the ground, reading displays for a user to read position data, communication interface for communicating such data to an external device (e.g. a laptop computer), power supply (e.g. external power or internal battery power). The overall composition and function of theodolites are generally known by the person skilled in the art and will not be described in this document.
One benefit of the present invention is that the pattern may be provided on load bearing elements in constructions of different applications wherein the invention may be applicable. For instance, in the case of a torque sensor, the pattern is provided on the shaft which in turn is part of the overall application wherein the shaft is located, in an articulating arm arrangement the pattern is provided on the elements taking up load forming the joints, in a bearing application the pattern may be provided on load bearing elements such as balls or cylinders forming part of ball or cylinder bearings. This benefit comes from the fact that the pattern may be provided either as part of the material of the object it self (such as dimples or indentations) or on a material resilient to mechanical wear attached to the object.
Generally this invention also has a benefit of being able to provide high speed and highly accurate measurements of absolute position data, however, the upper limit of the speed is limited to the pattern acquisition rate, for instance in case of an image acquisition system to providing images of the pattern, the frame rate of this image acquisition will set the upper limit on the rate. The present invention provide an accuracy that can exceed 10 fold the normal accuracy found in similar applications with more expensive and complex solutions in many applications.
It should be noted that the word “comprising” does not exclude the presence of other elements or steps than those listed and the words “a” or “an” preceding an element do not exclude the presence of a plurality of such elements. It should further be noted that any reference signs do not limit the scope of the claims, that the invention may be implemented at least in part by means of both hardware and software, and that several “means”, “units” or “devices” may be represented by the same item of hardware.
The above mentioned and described embodiments are only given as examples and should not be limiting to the present invention. Other solutions, uses, objectives, and functions within the scope of the invention as claimed in the below described patent claims should be apparent for the person skilled in the art.
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|Citing Patent||Filing date||Publication date||Applicant||Title|
|US8436736 *||Jun 7, 2011||May 7, 2013||Hon Hai Precision Industry Co., Ltd.||Temperature monitoring system and method|
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|Cooperative Classification||G01L3/12, G01D5/347, G06F3/0321|
|European Classification||G01D5/347, G01L3/12, G06F3/03H3|
|Aug 14, 2008||AS||Assignment|
Owner name: GCODER SYSTEMS AB, SWEDEN
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:NILSAGARD, JONAS;TAKMAN, OLLE;STENBERG, MANNE;REEL/FRAME:021391/0570;SIGNING DATES FROM 20080626 TO 20080811
Owner name: GCODER SYSTEMS AB, SWEDEN
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:NILSAGARD, JONAS;TAKMAN, OLLE;STENBERG, MANNE;SIGNING DATES FROM 20080626 TO 20080811;REEL/FRAME:021391/0570
|Dec 3, 2014||FPAY||Fee payment|
Year of fee payment: 4